The present invention relates to a distance detecting apparatus and method for a vehicle which successively measures the distance from a vehicle to a preceding vehicle running ahead thereof.
Some typical examples of such a distance detecting apparatus are disclosed in Japanese Patent Publication Nos. 63-38085 and 63-46363. The apparatuses disclosed therein commonly have a pair of first and second parallel optical systems having two convex lenses 101, 102 disposed in a horizontally aligned relation at a prescribed distance B away from each other, as shown in FIG. 7. A pair of separate image sensors 103, 104 are horizontally disposed at focal points of the lenses 101, 102 spaced a focal distance f from the locations of corresponding lenses 101, 102, respectively, for generating respective image signals representative of an object 105 such as a vehicle. A pair of A/D converters 106, 107 receive the image signals from the corresponding image sensors 103, 104 and convert them into digital signals which are then stored in a pair of corresponding memories 108, 109. A common microprocessor 110 takes out the digitized image signals stored in the memories 108, 109 and processes them for the purpose of calculating the prependicular distance L between the object 105 and the lenses 101, 102.
Specifically, the microprocessor 110 successively shifts the image signals read out from the image sensors 103, 104 and electrically superposes them one over the other, so that the distance L from the lenses 101, 102 to the object 105 is calculated based on the principle of triangulation using the following formula: EQU L=(f.times.B)/(a.times.P)
where a is a shift distance by which the image signals are moved to obtain the best match, and P is the pitch between picture elements in the image sensors 103, 104.
On the other hand, a typical method of following a preceding vehicle as captured by an image sensor or the like is disclosed in Japanese Patent Publication No. 60-33352. In this method, for the purpose of following a target on a display screen, an operator has to set a following gate or window on the display screen which encloses the target to be followed, while looking at the screen. In this case, most image signals of the background, which are noise in following the target image, are excluded from the window.
Using the distance detecting apparatus as described above, which successively detects the distance from a vehicle to a preceding vehicle, in combination with the above-described image following method, which continuously follows a specific target imgage, it is almost practically impossible for the driver to set a rather complicated following window or gate on a screen while driving the vehicle, as described in Japanese Patent Publication No. 60-33352. This poses a problem particularly from the safety point of view. In this connection, even if a rather simple window is employed for expediting and simplifying the driver's window setting operation, background images degrade the S/N ratio, thus making it difficult to follow the target image.